EFFECTS OF ROCKET EXHAUST PRODUCTS IN THE THERMOSPHERE AND IONOSPHERE John Zinn, C. Dexter Sutherland, Sidney N. Stone, and Lewis M. Duncan Los Alamos Scientific Laboratory, Los Alamos, New Mexico Richard Behnke Arecibo Observatory, Arecibo, Puerto Rico This paper reviews the current state of our understanding of the problem of ionospheric F-layer depletions produced by chemical effects of the exhaust gases from large rockets, with particular emphasis on the "Heavy Lift Launch Vehicles" (HLLV) proposed for use in the construction of solar power satellites. The currently planned HLLV flight profile calls for main second-stage propulsion at apogee. The second-stage engines deposit 9 x 10'51 H2 molecules between 74 and 124 km. Model computations show that they diffuse gradually into the ionospheric F region (i.e., above 200-km altitude), where they lead to weak but widespread and persistent depletions of ionization and continuous production of H atoms. The orbit-circularization burn deposits 9 x 10^9 exhaust molecules at about 480-km altitude. These react rapidly with the F2 region 0+ ions, leading to a substantial (factor of three) reduction in plasma density, which extends over a 1000- by 2000-km region and persists for four to five hours. Present understanding of ionospheric F-layer depletions caused by exhaust products from large rockets began with the observations by M. Mendil 1 o et al. of an abrupt decrease in vertical electron column density along the trajectory of the launch of Skylab I May 14, 1973. The ionospheric electron column density was observed to be reduced by 50% or more over a period commencing within ten minutes after the launch and persisting for about four hours. The effect was attributed to the chemical reaction of rocket exhaust molecules, primarily H20 and H2, with 0+, the dominant F2 layer ion. The main reactions are The severity, geographic extent, and duration of the F-layer depletions produced by the exhaust product molecules are determined by a combination of interacting processes, including chemistry, diffusion, gravitational settling, and advection by prevailing winds. We are studying these combined processes with the aid of an elaborate two-dimensional computer model, which has proven capable of reproducing the experimental data quite well. According to the model, the apparent four-hour duration of the Skylab ionospheric hole was due to winds that moved it out of the instrumented 1 ines-of-sight. The actual lifetime of the hole was probably 16 hours.
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